Shaft bearings are used to constrain a rotating shaft to maintain its axis of rotation. Such shaft bearings are used in motors, such as spindle motors, commonly found in computer equipment and audio systems. A typical structure for a shaft bearing includes two rings, bearings, and a retainer. The two rings are an inner ring, having a rotation groove on its outer surface, and an outer ring, having a corresponding rotation groove on its inner surface. The grooves and the axis of rotation are common to the rings. Between the two rotation grooves are a plurality of bearings, sometimes called ball bearings, which are evenly spaced apart circumferentially. The retainer is between the inner and outer rings and maintains even spacing of the bearings around the circumference of the rings. In this manner, the inner ring rotates with respect to the outer ring along a common axis by means of the evenly spaced apart bearings between the rotation grooves.
One type of retainer is a crown retainer. A crown retainer is typically molded from resin into a ring shape and includes a plurality of pockets equidistantly spaced around the circumference of the retainer. Each pocket retains a corresponding bearing to maintain the even spacing of the bearings around the rotation grooves. The pockets are open on one side of the retainer along the axial direction of the retainer. The inner surface of each pocket has a curvature corresponding to the curvature of the bearing.
The shaft bearing is assembled by inserting the bearings between the respective rotation grooves of the outer and inner rings, and inserting the retainer between the rings to snap each bearing into its corresponding pocket on the retainer. Upon mounting the retainer, grease is inserted into the shaft bearing, and a shield is mounted on the shaft bearing to close the gap between the inner and outer rings.
The grease is inserted onto the retainer between the inner and outer rings. The grease is inserted from the side of the retainer that has the pocket openings, and it is inserted onto the edge faces of the retainer between the pockets, where it adheres. A component of the grease is a low viscosity lubricating oil, called base oil, which soaks through from the grease and flows into the pockets as the retainer revolves around the axis of rotation. Since the bearings rotate in the retainer, the base oil in the interior of the pockets migrates between the rotation grooves of the inner and outer rings. In this manner, the base oil lubricates the rotation faces of the bearings in contact with the rotation grooves.
Some shaft bearings, however, do not allow insertion of the grease from the side of the retainer having the pocket opening. Examples of such shaft bearings have multiple coaxial rows of bearings. One such example is a shaft bearing having two coaxial rows of bearings between the inner and outer rings. Each row of bearings has a respective retainer that is inserted between the rings to snap the two rows of bearings into place. But the pocket openings of the two retainers face each other in this assembly. Access to the retainers is only to the respective sides of the retainers that are opposite to the pocket openings. As such, the grease is not near the pockets as they move around the circumference of the grooves, and it takes a relatively long time for sufficient base oil to reach the surface of the bearings.
In this case, the lack of sufficient lubrication reduces the life span of the shaft bearing or renders the shaft bearing immediately unusable. Moreover, the grease immediately scatters when the shaft begins to rotate and adheres to the outer ring and shield. Achieving a stable rotation with low torque is therefore difficult.
One proposed solution is to include channels between the pockets on the outer circumference of the retainer. Each channel runs between the edge faces of the retainer. Either the channel holds the grease or the grease is inserted through the channel to the pocket opening side of the retainer. Even so, it is difficult to align the nozzle of a grease gun with each channel, and the grease would adhere to the inner surface of the outer ring and not sufficiently utilize the channel.
A further proposed solution to the problems associated with the channels in the retainer is to form a relatively elongated nozzle access area that leads to each channel on the edge face opposite the pocket opening. Such a nozzle access area is described in Japanese Patent Publication No. JP 8-277843. The ejection opening of the nozzle may be easily positioned with respect to this relatively long nozzle access area, in contrast to the difficulty of positioning the nozzle with respect to the channels as described above. The easy positioning allows for the adequate insertion of grease.
Since grease is inserted from the nozzle access area up to the channel, however, this solution is inefficient because not all of the grease is used. Also, flow resistance of the grease is generated as the route traveled by the inserted grease lengthens, and the channel may still not receive sufficient grease.